X button in Wii U Gamepad doesn't work and it's "stuck"

Hello guys, i've got a problem with the X button of the Wii U gamepad: It doesn't work, and when I play Mario Kart 8, the reverse camera is always active, like if it was stuck.

Sometimes, it fixes itself, but i've noticed that everytime I charge the gamepad, it does it all over again.

I'm not used to opening things up and that $@$*, but I could do it if it can fix the problem.